1. Field of the Invention
The present invention relates to a fuel injection apparatus for mainly an internal combustion engine for injecting fuel of a low viscosity or lubricating ability such as gasoline or methanol at a high pressure of tens of atmospheres or more.
2. Description of the Related Art
When supplying fuel with a relatively high viscosity or lubricating ability such as gas oil to a diesel engine at a high pressure, the fuel itself becomes the lubricating oil of the fuel injection pump, so there is no need to supply any special lubricating oil to the fuel injection pump, but when injecting fuel of a relatively low viscosity or lubricating ability such as gasoline or methanol into cylinders of an internal combustion engine under high pressure, that fuel does not act to lubricate the sliding portions between the plunger of the fuel injection pump and the pump cylinder receiving the same, so it is necessary to supply a lubricating oil other than the fuel to the sliding portions.
In such a case, the problem arises that when the lubricated sliding surfaces of the fuel injection pump are exposed by the movement of the plunger, the fuel dissolves into the lubricating oil film, so the entire amount of the lubricating oil ends up diluted by the fuel and deteriorated, the lubricating ability of the lubricating oil falls, and wear of the fuel injection pump is invited.
Further, in a fuel injection pump which raises relatively flow viscosity fuel such as gasoline or methanol to a high pressure, fuel easily leaks from the sliding portions of the plunger and pump cylinder, so there is the problem that it is relatively difficult to maintain a high precision of adjustment or distribution of the fuel by the fuel injection pump.